Mars manned exploration missions - logic behind a Hermes style vehicle?

[Halo_003]

So, I'm curious about how smart it would be for the world's space agencies to collaborate on building a Hermes style transport ship for manned Mars exploration(picture below).

 

 

My thought is, if they all get together, splurge and build a highly efficient/designed to last ship where the computer systems and electronics are easy to replace, then it could also likely be used for beyond Mars exploration missions. Such as a flyby of Venus, etc. Yes it would be required to overengineer some systems and to include a nice buffer on the amount of dV onboard, but I was curious if otherwise it makes sense to do it this way? Am I totally off base here or does that actually make a decent amount of sense?

[Nibb31]

The ship is pretty realistic, if you take into account the magic propulsion. In reality, major part of such a vehicle would be tankage, even if it had SEP. Also, it would probably need more solar panels. The rotating section is unnecessary, but people have become accustomed to the idea that spaceships need a rotating section for artificial gravity.

The movie doesn't detail the actual mission architecture. It seems like the MAVs and maybe some cargo landers are prepositioned before the arrival of the crew, so we can assume that they use some other vehicle for cargo and MAV delivery. We also don't know what the crew uses for landing or whether that vehicle is prepositioned in orbit or if the Hermes carries it along.

[sevenperforce]

A handful of thoughts...

To start with, "the world's space agencies" basically means the US and Russia, and maybe China. Nobody else has anywhere near the budget for this sort of thing. And since the US and Russia aren't really getting along right now...yuck.

This would be more of an interplanetary space station than a transfer vehicle, so if we want it to last for a while, we're going to need to think long-term. Chemical propulsion probably isn't the best option; we'd need to wait until VASMIR engines had been integrated into the ISS and all the kinks had been worked out. Micrometeoroid shielding is another problem if it's going to be spending really long periods of time coasting around the solar system.

Another possible propulsion mode would be to have an entire engine module which received liquid water from asteroids or the moon, so that the fuel supply would be separate from the propellant supply.

You'd need fixed docking points for spacecraft and attachment points to strap on ascent/descent vehicles, plus a full-size robotic arm attachment system. Depending on the size we're dealing with, it might also make sense to throw some retractable solar sails on there.

Edited February 1, 2016 by sevenperforce

[benjee10]

The ship is actually nuclear powered so if anything it has too many solar panels. I'm not an expert on electric propulsion by any means but I think that the amount of fuel is about right for a ship this size, the amount of power and the length of the trip. Someone would have to do some fact checking there though. Overall, however, it's surprisingly realistic overall considering it's a hollywood creation. The only things that really bug me are the offset module at the front (why? what could you possibly gain by having the front of the ship lower than the back that could justify the stability and CoT problems it'd cause?) and the fact that it has far more habitable space than would be needed. The rotating gravity drum is a bit questionable too. The design looks plausible but I'm not sure how realistic maintaining a rotating pressurised joint in vacuum for so long would be. The curved truss would be a nightmare to launch too. 

In terms of the idea of the ship - it's absolutely a good idea. Why build a new transfer vehicle every time you want to go somewhere when you could have a slightly bigger, more expensive ship which can make the trip several times? I can see a similar system being adopted if early Mars missions use NTRs or less efficient propulsion systems which require tanks to be jettisoned or can't be refurbished, with the propulsion module being discarded on return to Earth and being refitted with a new one between trips so that at least some of the ship is reused. 

[tater]

Yeah, this is a totally different idea than Mars DRA 5. The capsule (?) at the front of hermes is a little odd with the 2 cupolas behind it since the point of the capsule is Earth reentry, and the current plans are all for direct reentry. 

[Nibb31]

Isn't the Hermes reusable? I don't think the capsule at the front reenters. I would think that they dock at an EML gateway and return on an Orion-like vehicle.

[tater]

Yeah, they said it was for the entire series of missions. I know it's not supposed to be Orion (even though in the movie version they showed the Orion test flight launch). That said, look at it, it's a capsule. I realize that it's just what the CGI artist decided looked cool.

So the mission plan requires a propulsive Earth orbital insertion for the Hemes cycler, then a separate craft to deliver the new crew, and take the old crew back I guess.

[sevenperforce]

1 hour ago, benjee10 said:

The ship is actually nuclear powered so if anything it has too many solar panels. I'm not an expert on electric propulsion by any means but I think that the amount of fuel is about right for a ship this size, the amount of power and the length of the trip. Someone would have to do some fact checking there though. Overall, however, it's surprisingly realistic overall considering it's a hollywood creation. 

I haven't read the book. Is it radiothermally powered, or powered by an actual nuclear-thermal rocket?

Ostensibly, the Hermes only carries the fuel for the transfer from LEO to LMO and back. The MAVs and Martian habs were apparently placed via unmanned missions some time earlier, while the crew is ferried to the Hermes in an ordinary chemical rocket and uses a capsule for descent. Refueling the Hermes between missions would probably happen along with the crew-ferrying trips. In the movie (and I assume the book as well), Mark Watney uses a buried radiothermal generator as a heat source and mentions they had brought it with them...does it ever say where this came from?

The curved trusses are definitely unlikely; even if you must have toroidal rotating hab, there'd be no reason not to join them with straight trusses.

If you're going to have a rotating hab for gravity simulation, wouldn't it make more sense to just do a vertically stacked system, rather than a toroidal one? I suppose the toroidal arrangement allows for more floor space and a uniform artificial gravity, but a stacked system would be so much easier to construct.

[MatttheCzar]

It has a nuclear reactor for the ship.  The RTG is for first experiments and the Hab startup.

[Spaceception]

 I think It's pretty realistic, and the odds are good that we'll use something similar after a couple of manned Mars missions, it's like a bigger $$$$ version of the Nautilus-X.

And yes, I'm using blue writing, I like the color.

Edited February 1, 2016 by Spaceception

[benjee10]

50 minutes ago, tater said:

Yeah, they said it was for the entire series of missions. I know it's not supposed to be Orion (even though in the movie version they showed the Orion test flight launch). That said, look at it, it's a capsule. I realize that it's just what the CGI artist decided looked cool.

That's the command deck, which most movie ships tend to have; it gives a compositional focus for the audience (we're naturally drawn to looking at windows and such) and provides interesting interior sets which you can do nice lighting things with by pouring light in through the window frames. Doesn't look like a detachable capsule; it's just a cone-shaped flight deck which does make sense from a design standpoint since it allows forward facing visibility without the awkwardness of a cupola-type design if you're planning on putting a docking port/airlock on the front of it. 

The bits of the movie that took me out of it the most and seemed most contrived weren't actually any of the tech designs; they all seem pretty realistic. It was things which were clearly done to look cool, like having an astronaut on EVA when the supply ship docks 'backing it up' for some reason, and that for some strange reason they use an MMU at the end while still tethered when the whole point of the MMU was to allowed untethered free flight. There's literally no point in having one if you're going to be tethered to the station since you'd only be floating a few meters from the ship at most anyway (the long tether at the end they explained was made from many other tethers joined together, which clearly wasn't a regular occurrence). Kind of similar to how in 2001 the little EVA pods, cool as they are, serve almost no functional purpose since the astronauts take them a few hundred meters from the ship and then propel themselves out of them back towards the ship. You might as well have just opened the hatch and propelled yourself around on your own. The pods just take up unnecessary space and add the complexity of having to depressurise and then repressurise the entire pod bay instead of one airlock. 

[sevenperforce]

Also how the captain insisted on using the MMU herself in place of the person who actually had the most training...

[tater]

Or landing among mesas, lol  Clearly that was to make the most of a stunning film location, a NASA landing ellipse would be rather more boring.

 

[DerekL1963]

3 hours ago, sevenperforce said:

This would be more of an interplanetary space station than a transfer vehicle, so if we want it to last for a while, we're going to need to think long-term. Chemical propulsion probably isn't the best option; we'd need to wait until VASMIR engines had been integrated into the ISS and all the kinks had been worked out.

Actually, we need to wait until VASMIR engines with sufficient thrust and sufficiently light power supplies have been developed.   We're nowhere near either.  VASMIR is basically a very fancy ion engine, and even in "high thrust" it doesn't produce very much thrust at all.  (The 200kw system intended for testing on ISS only produces a pound or so of thrust.)

[sevenperforce]

Would an NTR then be a better choice for the interplanetary space station transfer ship thing?

This is only tangentially related...but in analogy to a hybrid rocket that uses a solid fuel and liquid oxidizer, I wonder if it would be feasible to build a hybrid nuclear rocket, using lithium-6 hydride saltwater and natural uranium. Lithium-6 could be kept in solid pellets and dissolved in ordinary water as needed for each burst of thrust. Dissolving lithium-6 into water produces gaseous hydrogen (used to provide pressure to run the pump) and lithium-6 hydride saltwater, which would pass into the nuclear reactor, absorb low-energy neutrons from radioactive decay of the uranium, and decay into hydrogen, tritium, and fast neutrons, greatly increasing the energy released.

[DerekL1963]

37 minutes ago, sevenperforce said:

Would an NTR then be a better choice for the interplanetary space station transfer ship thing?

From the point of view of performance and technological availability, yes.   From the point of view of budget and political complications, not so much.   But NTR has the virtue of actually existing.

39 minutes ago, sevenperforce said:

 

[fredinno]

4 hours ago, Nibb31 said:

The ship is pretty realistic, if you take into account the magic propulsion. In reality, major part of such a vehicle would be tankage, even if it had SEP. Also, it would probably need more solar panels. The rotating section is unnecessary, but people have become accustomed to the idea that spaceships need a rotating section for artificial gravity.

The movie doesn't detail the actual mission architecture. It seems like the MAVs and maybe some cargo landers are prepositioned before the arrival of the crew, so we can assume that they use some other vehicle for cargo and MAV delivery. We also don't know what the crew uses for landing or whether that vehicle is prepositioned in orbit or if the Hermes carries it along.

Well, the rotating section kind of serves the purpose of mitigating the effects of Zero-G. The only problem I have is that you'd have to pass through the Van Allen a lot, since this is powered by IONs.

4 hours ago, sevenperforce said:

A handful of thoughts...

To start with, "the world's space agencies" basically means the US and Russia, and maybe China. Nobody else has anywhere near the budget for this sort of thing. And since the US and Russia aren't really getting along right now...yuck.

This would be more of an interplanetary space station than a transfer vehicle, so if we want it to last for a while, we're going to need to think long-term. Chemical propulsion probably isn't the best option; we'd need to wait until VASMIR engines had been integrated into the ISS and all the kinks had been worked out. Micrometeoroid shielding is another problem if it's going to be spending really long periods of time coasting around the solar system.

Another possible propulsion mode would be to have an entire engine module which received liquid water from asteroids or the moon, so that the fuel supply would be separate from the propellant supply.

You'd need fixed docking points for spacecraft and attachment points to strap on ascent/descent vehicles, plus a full-size robotic arm attachment system. Depending on the size we're dealing with, it might also make sense to throw some retractable solar sails on there.

Actually, NASA can't cooperate with China right now either due to politics, so NASA would just make this with Japan and Europe, and possibly India, if this is "International".

42 minutes ago, sevenperforce said:

Would an NTR then be a better choice for the interplanetary space station transfer ship thing?

This is only tangentially related...but in analogy to a hybrid rocket that uses a solid fuel and liquid oxidizer, I wonder if it would be feasible to build a hybrid nuclear rocket, using lithium-6 hydride saltwater and natural uranium. Lithium-6 could be kept in solid pellets and dissolved in ordinary water as needed for each burst of thrust. Dissolving lithium-6 into water produces gaseous hydrogen (used to provide pressure to run the pump) and lithium-6 hydride saltwater, which would pass into the nuclear reactor, absorb low-energy neutrons from radioactive decay of the uranium, and decay into hydrogen, tritium, and fast neutrons, greatly increasing the energy released.

Good luck making that work.

[Wjolcz]

I am not 100% sure about Hermes' propulsion, but wasn't it said in the book that it was some sort of VASIMR?

Also, in terms of looks Nautilus-X > Hermes. Wish the ship in the film was more based on some modular structure similar to Nautilus than a weird off-center front thing. I mean, it looks pretty cool anyway but I'm a fanboy of compact spaceships with variable and easy to rearrange configuration.

Yet another edit: Isn't that triple antenna dish a nod to 2001? Looks pretty similar to the one Discovery had. Or is it just the most logical thing to have on a massive spaceship?

Edited February 2, 2016 by Veeltch

[Bill Phil]

I think that a small flotilla of two would be a bit better. Maybe 3, but only if it's possible. I also recommend a trailer layout, where the engines pull the spacecraft, rather than pull. Like the ship in avatar, but probably a VASIMR-like propulsion system. Idk the power source, but we are in the future. Now, having two, especially in formation, would allow us to have one fail in some way, and the other can still accomplish the mission. If we're smart, we would put a station in Mars orbit, which would have a reuasable lander (if possible).

/joke

Of course, if the Q-Drive works, we can use that.

/joke

[magnemoe]

4 hours ago, benjee10 said:

That's the command deck, which most movie ships tend to have; it gives a compositional focus for the audience (we're naturally drawn to looking at windows and such) and provides interesting interior sets which you can do nice lighting things with by pouring light in through the window frames. Doesn't look like a detachable capsule; it's just a cone-shaped flight deck which does make sense from a design standpoint since it allows forward facing visibility without the awkwardness of a cupola-type design if you're planning on putting a docking port/airlock on the front of it. 

The bits of the movie that took me out of it the most and seemed most contrived weren't actually any of the tech designs; they all seem pretty realistic. It was things which were clearly done to look cool, like having an astronaut on EVA when the supply ship docks 'backing it up' for some reason, and that for some strange reason they use an MMU at the end while still tethered when the whole point of the MMU was to allowed untethered free flight. There's literally no point in having one if you're going to be tethered to the station since you'd only be floating a few meters from the ship at most anyway (the long tether at the end they explained was made from many other tethers joined together, which clearly wasn't a regular occurrence). Kind of similar to how in 2001 the little EVA pods, cool as they are, serve almost no functional purpose since the astronauts take them a few hundred meters from the ship and then propel themselves out of them back towards the ship. You might as well have just opened the hatch and propelled yourself around on your own. The pods just take up unnecessary space and add the complexity of having to depressurise and then repressurise the entire pod bay instead of one airlock. 

Yes, having an cone let you have visibility of the docking. 
No you don't need an real bridge of an spaceship, something like an command center on a warship makes more sense. Yes you could control it from an laptop but having an command center make communication easier. 
However bridges are look cool, not having an cool bridge make taxpayers feel cheated and its has few downsides over an command center on a civilian ship.
It might have been taken from an sort of space shuttle too. 

Has not read the book but I think it had an ship spinning along the long axis with engine in one end and crew module in the other. This save weight but does not look so cool. 
Hermes has the benefit of making it easy to add new payloads too. More practical if you plan on using it for a lot of missions. 

[tater]

What % of a Mars flight is VASIMR supposed to be under acceleration? Strikes me that you'd not spin up that middle section except during a coast phase.

[SargeRho]

22 minutes ago, tater said:

What % of a Mars flight is VASIMR supposed to be under acceleration? Strikes me that you'd not spin up that middle section except during a coast phase.

A VASIMR mission to mars would probably follow a brachistochrone trajectory, but the Hermes uses Xenon Ion Engines, not VASIMR engines.

I think this kind of design would have made more sense for the Hermes, though: http://www.deviantart.com/art/Hermes-Rotate-564814706

[Temstar]

The movie Hermes had an onboard nuclear reactor to power its engine (VASIMR or regular ion, I'm not sure, but it's certainly a high isp low thrust engine). It's a bit strange that it also had ISS style solar panels to power the rest of the ship since presumably it would be easier to just bring a reactor powerful enough to power both the engine and the rest of the ship, but I guess the artists wanted to show the solar panels so we get a sense of technological progression from ISS to Hermes.

Having a reactor onboard raises other issues. For one it would need a lot more radiators than what was shown as per the picture @SargeRho linked. Secondly unless the reactor is ungodly heavy by spacecraft standards it won't have shielding all the way around like a marine reactor. Instead it would use a shadow shield to protect just the structure of the ship. This seems to be the case in the movie as the reactor is located all the way at the back of the ship next to the engine, while the crewed section is on the other end of the ship. So presumably just above the reactor is the shadow shield. Notice how the Hermes on DA by francisdrakex had these funny looking radiators arranged in a triangular pattern? That's so they all remain in the radiation shadow cast by the shadow shield. If you go beyond that limit you will pick up a lethal dose before you can blink.

Of course if your ship is protected by a shadow shield then what you don't want to do is go on a EVA out the side of the ship 300m away, or have a manned MAV fly by at similar distance. Both of them would be dead rather quickly.

[tater]

Either way, the vessel is under constant acceleration. So the floor would not strictly speaking be the floor do to the additional force vector.

[fredinno]

12 minutes ago, tater said:

Either way, the vessel is under constant acceleration. So the floor would not strictly speaking be the floor do to the additional force vector.

Ion have a low enough thurst it'd likely not matter.